Ruby v3.4 stacktrace uses single-quote vs backtick

Since this change [1], lines in the stacktrace use an opening
single-quote instead of a backtick to delimit the method name, e.g.

    foo.rb:5:in 'Foo#bar': boom! (RuntimeError)

Instead of:

    foo.rb:5:in `Foo#bar': boom! (RuntimeError)

This commit makes a relevant assertion specific to the current Ruby
version.

This is somewhat similar to the fixes I put in place in #672, although
those were later considerably simplified in #680. Unfortunately I can't
see a way to achieve a similar simpification in this case.

[1]: https://bugs.ruby-lang.org/]issues/16495

test/integration/shared_tests.rb

@@ -1,5 +1,6 @@
 require 'test_runner'
 require 'execution_point'
+require 'mocha/ruby_version'
 
 # rubocop:disable Metrics/ModuleLength
 module SharedTests
@@ -156,6 +157,8 @@ def test_real_object_unsatisfied_expectation
   end
 
   def test_real_object_expectation_does_not_leak_into_subsequent_test
+    opening_quote = Mocha::RUBY_V34_PLUS ? "'" : '`'
+
     execution_point = nil
     klass = Class.new
     test_result = run_as_tests(
@@ -170,7 +173,7 @@ def test_real_object_expectation_does_not_leak_into_subsequent_test
     assert_errored(test_result)
     exception = test_result.errors.first.exception
     assert_equal execution_point, ExecutionPoint.new(exception.backtrace)
-    assert_match(/undefined method `foo'/, exception.message)
+    assert_match(/undefined method #{opening_quote}foo'/, exception.message)
   end
 
   def test_leaky_mock